LTC4069-4.4 Linear Technology, LTC4069-4.4 Datasheet - Page 8

• Manufacturer Part Number: LTC4069-4.4
• Description: Standalone 750mA Li-Ion Battery Charger in 2 x 2 DFN
• Manufacturer: Linear Technology

OPERATION
LTC4069-4.4
temperatures for a given application with the assurance
that the charger will automatically reduce the current in
worst-case conditions.
The charge cycle begins when the voltage at the V
rises above 3.5V and approximately 80mV above the BAT
pin voltage, a 1% program resistor is connected from the
PROG pin to ground and the NTC pin voltage stays between
0.76 • V
If the BAT pin voltage is below 2.9V, the charger goes into
trickle charge mode, charging the battery at one-tenth the
programmed charge current to bring the cell voltage up to
a safe level for charging. If the BAT pin voltage is above
4.3V, the charger will not charge the battery as the cell
is near full capacity. Otherwise, the charger goes into the
fast charge constant-current mode.
When the BAT pin approaches the fi nal fl oat voltage (4.4V),
the LTC4069-4.4 enters constant-voltage mode and the
charge current begins to decrease. When the current
drops to 10% of the full-scale charge current, an internal
comparator turns off the N-channel MOSFET on the CHRG
pin and the pin assumes a high impedance state.
An internal timer sets the total charge time, t
4.5 hours). When this time elapses, the charge cycle
terminates and the CHRG pin assumes a high impedance
state. The charge cycle will automatically restart if the
BAT pin voltage falls below V
To manually restart the charge cycle, remove the input
voltage and reapply it, or momentarily fl oat the PROG pin
and reconnect it.
Programming Charge Current
The charge current is programmed using a single resistor
from the PROG pin to ground. The battery charge current is
1000 times the current out of the PROG pin. The program
resistor and the charge current are calculated using the
following equations:
The charge current out of the BAT pin can be determined
at any time by monitoring the PROG pin voltage and using
the following equation:
8
R
PROG
CC
=
and 0.35 • V
1000
•
I
CHG
1
V
CC
,
I
or below 0.016 • V
CHG
=
RECHRG
1000
R
PROG
V
(typically 4.3V).
TIMER
CC
.
(typically
CC
pin
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the
input voltage and keeps the charger in undervoltage
lockout until V
80mV above the BAT pin voltage. The 3.6V UVLO circuit
has a built-in hysteresis of approximately 0.6V and the
automatic shutdown threshold has a built-in hysteresis
of approximately 50mV. During undervoltage lockout
conditions, maximum battery drain current is 4μA and
maximum supply current is 11μA.
Shutdown Mode
The LTC4069-4.4 can be disabled by fl oating the PROG pin.
In shutdown mode, the battery drain current is reduced to
less than 1μA and the supply current to about 20μA.
Timer and Recharge
The LTC4069-4.4 has an internal termination timer that
starts when an input voltage greater than the undervoltage
lockout threshold is applied to V
shutdown and the battery voltage is less than the recharge
threshold.
At power-up or when exiting shutdown, if the battery voltage
is less than the recharge threshold, the charge time is set
to 4.5 hours. If the battery temperature is either too high
or too low, the timer will pause until the battery returns
to normal temperature. If the battery is greater than the
recharge threshold at power-up or when exiting shutdown,
the timer will not start and charging is prevented since the
battery is at or near full capacity.
Once the charge cycle terminates, the LTC4069-4.4
continuously monitors the BAT pin voltage using a
comparator with a 2ms fi lter time. When the battery
voltage falls below 4.3V (which corresponds to 80% to
90% battery capacity), a new charge cycle is initiated and
a 2.25 hour timer begins. This ensures that the battery is
kept at, or near, a fully charged condition and eliminates
the need for periodic charge cycle initiations. Also, if the
I
BAT
=
R
V
PROG
PROG
CC
• 1000
rises above 3.6V and approximately
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CC
, or when leaving
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